Barium magnesium aluminate phosphors are known and widely used as blue-emitting phosphors, especially for triband white fluorescent lamps. This is due to the relatively high quantum efficiency and the appropriate spectral distribution of barium magnesium aluminate phosphors. A basic disclosure of barium magnesium aluminate phosphors can be found in U.S. Pat. No. 4,216,408.
An important disadvantage of barium magnesium aluminate phosphors is, however, the insufficient stability over the time of operation, especially in case of excitation with VUV radiation with a wavelength below 200nm. This insufficient stability or maintenance results in a deterioration of quantum efficiency as well as in a shift of the emission spectrum. Consequently, phosphor blends and lamps employing conventional barium magnesium aluminate phosphors show a colour shift to green with longer operation times. This problem is the more severe the larger the fraction of barium magnesium aluminate phosphor in the blend, i.e. the higher the correlated colour temperature. Such higher colour temperatures, however, are typical for displays and display illumination systems.